(1) Field of the Invention
The present invention relates to a carbon composite material having gas non-permeability and high electroconductivity, as well as to a process for production thereof.
(2) Description of the Prior Art
Carbon materials having gas non-permeability find main applications such as member for heat exchanger, material go for semiconductor production, part of fuel battery, and the like. Gas non-permeable carbon materials of low cost and excellent performance have been desired.
Gas non-permeable carbon materials have heretofore been produced by, for example, (1) a process which comprises impregnating a carbon material such as glassy carbon sheet, graphite or the like with a thermosetting resin [Japanese Patent Application Kokai (Laid-Open) No. 153877/1990], (2) a process which comprises coating an expanded graphite molded material with a resin and firing the coated molded material up to about 2,0000.degree. C. in an inert gas atmosphere [Japanese Patent Application Kokai (Laid-Open) No. 127284/1985], or (3) a process which comprises impregnating an expanded graphite molded material with a thermosetting resin and hot-pressing the impregnated molded material [Japanese Patent Application Kokai (Laid-Open) No. 12672/1985].
The above processes (1) to (3), however, each have problems. In the process (1), the glassy carbon sheet, although having sufficient gas non-permeability and electroconductivity, takes time in firing and invites a high cost and, moreover, is unable to produce a material of complicated shape. In the process (2) which comprises coating expanded graphite with a thermosetting resin and firing the coated expanded graphite in an inert gas, the necessity of the coating step makes the process complicated and, moreover, formation of a carbon layer having no pinhole is very difficult and no sufficient gas non-permeability can be obtained. In the process (3) which comprises impregnating an expanded graphite sheet with a resin, the necessity of the impregnation step makes the process complicated and, moreover, no sufficient gas non-permeability is achieved.
In order to solve these problems, there were proposed, for example, (4) a process which comprises placing an expanded graphite powder and an organic binder in a solvent, drying and grinding the resulting mixture to form secondary particles consisting of an expanded graphite powder and an organic binder, and molding the secondary particles to form an expanded graphite molded material [Japanese Patent Application Kokai (laid-open) No. 32517/1979] and (5) a process which comprises mixing expanded graphite and an organic binder and molding the resulting mixture [Japanese Patent Application Kokai (laid-Open) Nos. 49656/1983, 254363/1987 and 154467/19891].
Expanded graphite of ordinary use, however, has no good miscibility with organic binder. Use of a large amount of expanded graphite for high electroconductivity results in insufficient gas non-permeability. Use of a small amount of expanded graphite for high gas non-permeability results in insufficient electroconductivity. Thus, development of a carbon material having both high gas non-permeability and electroconductivity has been desired.